Fuel mixture cited in plane crash reports

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The pilots of a plane that crashed shortly after takeoff from Lake Tahoe Airport in August, killing all five people onboard, expressed concerns about the craft's fuel/air mixture prior to departing, according to a preliminary report on the crash.

The National Transportation Safety Board also cited an improper fuel/air mixture as a contributing factor in a July 2009 crash at Lake Tahoe Airport that killed the aircraft's pilot.

The report on the Aug. 25 crash is preliminary and does not list a cause, but does say that pilots mentioned the difficulty in establishing the right fuel/air mixture at high altitude upon landing earlier that day.

"While taxiing to the ramp, the airplane's engine shutdown and it took numerous attempts for the pilots to restart it," according to the preliminary report. "Upon parking, the pilots reported to the attendants that the airplane's fuel/air mixture was difficult to establish at such a high density altitude and that if you operate the engine too lean its temperature will exceed normal operation parameters."

"Too lean" refers to a situation where an engine has too much air, relative to fuel, for ideal operation. "Density altitude" is a measure of altitude, temperature and humidity, according to the Federal Aviation Administration.

"High density altitude" refers to low-density air, which impacts aerodynamic performance and decrease the engine's horsepower, requiring adjustments to the plane's fuel/air mixture for proper operation, according to the FAA.

Surveillance footage from the airport from the August crash shows a blinking light on the plane level off before a flash of light occurs in the area of the crash site, according to the report. Several witnesses said they noticed the engine was not producing full power before the accident.

A malfunctioning carburetor and pilot error were determined to be the causes of a July 5, 2009, crash that killed pilot and Davis resident Casey William Daggett, 41, according to a report from the NTSB. The report was adopted by the board in August.

High-density altitude is also believed to be a factor in that crash.

Witnesses told investigators they saw the plane climb to about 100 feet with its nose unusually high up in the air before falling to the left and crashing. The malfunctioning carburetor likely caused the plane to have less air than necessary for ideal operation, according to NTSB's report.

"A partial loss of engine power due to a malfunctioning carburetor and the pilot's failure to maintain adequate airspeed while maneuvering to return to the runway," according to the report. "Contributing to the accident was the high density altitude."